Re: Worm fabrication (was : RE: ATM The Big Dob Two-Step (-per drive))

[andydtg@phoenix.net]

Carl Brennan wrote,

>I find this thread on worm drives facinating as I am interested in adding a
>drive
>to my dec. axis. Is it possible for a normal mortal like myself to make his own
>worm and gear or is the precision it requires too exacting and, if not, how
does
>one best go about it ??

Well, I hope this doesn't make me an abnormal
mortal but I do make my own worm gears, see recent posts
on the subject. This was the result of considerable 
experimentation and works well enough for me to make these
gears available to other ATM's at reasonable prices:

The gearhob technique I use now uses Acme threaded rod (1/2-10)
which has a tooth profile almost exactly like that of a 20 deg 
pressure angle actual worm gear. I mount the gear blank
on an extremely precise rotary milling table (+/- 5 arc sec)
and motor drive the table, with the acme tap rotating at
an integer fraction multiple of the reduction of the mill
table. The tap is fed radially inwards into the plastic gear
blank and gradually cuts the exact pitch and depth teeth
into it, as the same motor drives the table and the tap
in synch via a chain sprocket drive. 

I use these gears in my smaller alt-az computer driven
mounts, as well as to make focal plane rotators.

The precision of the gears is largely dependent on 
the quality of the rotary table and how well built
the hobbing machine is.



Andy Saulietis / DTG Alt-Az-Fp Drive Systems
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax